This invention relates generally to gas turbine engines and more particularly to bolted joints for joining adjacent rotor disks in such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and the mixture is ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to drive the compressor and provide useful work such as powering an aircraft in flight. The compressor and turbine sections each include a plurality of rotor disks that are joined together for rotation about the engine""s centerline axis. Each rotor disk comprises a central bore region, a disk rim from which a plurality of radially extending blades are supported, and a web joining the bore and rim. The bore and web are typically much more massive than the disk rim to accommodate the stresses to which the disk is subjected.
Rotating disks, particularly those in the high pressure turbine section of an engine, develop high radial thermal gradients during transient operation because of exposure of the disk rim to hot gases. In this case, the rim of the disk has a quick thermal response (i.e., temperature increase) while the web and bore react more slowly due to their high relative mass and their lower temperature environment. The thermal gradient creates large tangential and radial stresses in the web and bore of the disk that are magnified by any stress concentrations such as holes, fillets and the like.
A significant challenge in disk design is to connect multiple disks together without developing high stresses. One method of connection is through the use of bolted joints connecting adjacent disks. Often, at least one of the disks must be bolted through the disk web because of space limitations. In such instances, the bolt holes are located in regions of high thermal gradient and produce high concentrated stresses. This limits the allowable time of operation of the rotor hardware.
One approach to reducing bolt hole stress is to balance the radial and tangential stresses by modifying the hole pattern design, i.e., the number of holes, hole spacing, hole diameter and hole length. Generally, a bolted joint having more holes will produce lower mechanical stresses in the tangential direction but will result in higher radial stress. For every hole pattern design, there exists a certain quantity of holes that will balance the tangential stress at the top or bottom of the hole with the radial stress at the sides of the hole. However, modifying the hole pattern design to balance the radial and tangential stresses typically results in increased disk weight and even slower transient thermal response of the disk web and bore. Accordingly, there is a need for an improved method of reducing bolt hole stresses.
The above-mentioned need is met by the present invention, which provides a bolted joint for connecting first and second rotor disks in a gas turbine engine. The bolted joint includes a bolt hole formed in the first rotor disk and a bolt disposed in the bolt hole such that a channel is defined between the bolt and the bolt hole. A first abutment is attached to a first end of the bolt, and a second abutment is attached to a second end of the bolt. A first passage associated with the first abutment provides fluid communication with the channel, and a second passage associated with the second abutment provides fluid communication with the channel. Hot fluid passing through the channel reduces thermal gradients in the first rotor disk.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.